De Vaucouleurs Profile Research Articles

US 3215: AN ACTIVE GE2 GALAXY

ABSTRACT The object US 3215 is an optically variable galaxy with very broad Balmer lines, relatively strong forbidden lines and a weak UV-excess continuum. It has been classed as a Seyfert 1 galaxy. We report that optical CCD images taken in excellent seeing reveal a central mini-quasar in an elliptical galaxy with a de Vaucouleurs profile extending across an angular diameter of ∼ 13 arcsec. This corresponds to a linear size of almost 50 kpc (Ho = 50 km /sec/Mpc). Our data indicate that the host galaxy is of type gE2 and is the gravitational center of a cluster of galaxies. A companion galaxy is observed at a projected distance of 24 kpc. H and K magnitudes were obtained and the index H - K is consistent with quasar colors. A VLA snapshot at 1425 MHz gives an upper limit to radio emission at a flux level of 0.2 mJy beam -1 that is consistent with the Sy 1 designation. Thus US 3215 appears to be an active broad-line cluster gE2 galaxy.

A New Model of the Gravitational Lens 0957+561 and a Limit on the Hubble Constant

view Abstract Citations (115) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A New Model of the Gravitational Lens 0957+561 and a Limit on the Hubble Constant Grogin, Norman A. ; Narayan, Ramesh Abstract We present a simple mass model for the lensing galaxy in the gravitationally lensed quasar 0957 + 561. We represent the galaxy as a softened power-law sphere (SPLS), a generalization of the singular isothermal sphere with three parameters-ρ_0_, the central density; θ_c_, the angular core radius; and η, the radial index, which is defined such that mass increases as reta^ at large radius. As in previous studies, we approximate the galaxy cluster surrounding the lensing galaxy by means of a quadratic potential described by its convergence κ and shear γ. A feature of the model is that it does not require a large central compact mass. We fit the model to a recent high-resolution VLBI map of the two images of 0957+561. The data provide a number of independent constraints, and the model fit has 6 degrees of freedom, which is a significant improvement over previous models. Although the reduced χ^2^ of the best-fit model is only 4.3, nevertheless we obtain a tight constraint on the radial index, 1.07 < η < 1.18, at the 95% confidence level. Thus, the galaxy has mass increasing slightly more rapidly than isothermal (η = 1) out to at least 15 h^-1^ kpc. Since the light from the galaxy follows a de Vaucouleurs profile, we deduce that the mass-to-light ratio of the galaxy increases rapidly with increasing radius. We also obtain an upper limit on the core radius, namely θ_c_ < 0.11" or linear core radius < 330 h^-1^ pc. We use the model to calculate the Hubble constant H_0_ as a function of the time delay ATBA {DELTA}t_BA_ between the two images. We obtain H_0_ = (60.5^+5.3^_-2.2_)(1 - κ)({DELTA}t_BA_/1.5 yr)^-1^ km s^-1^ Mpc^-1^ , or = (82.5^+7.2^_-3.0_)(1 - κ)({DELTA}t_BA_/1.1 yr)^-1^ km s^-1^ Mpc^- 1^ Once {DELTA}t_BA_ is measured, this will provide an upper bound on H_0_ since κ cannot be negative. In addition, the model degeneracy due to κ can be eliminated if the one-dimensional velocity dispersion σ of the lensing galaxy is measured. In this case, we find that H_0_ = (60.5^+6.4^_-4.1_)(σ/322 km s^-1^)^2^({DELTA}t_BA_/1.5 yr)^- 1^ km s^-1^ Mpc^-1^, or =(82.5^+8.7^_-5.6_)(σ/322 km s^-1^)^2^({DELTA}t_BA_/1.1 yr)^-1^ km s^-1^ Mpc^-1^. We find that these results are virtually unchanged if we include the ellipticity of the lensing galaxy or clumpiness of the lensing cluster. Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177302 Bibcode: 1996ApJ...464...92G Keywords: COSMOLOGY: DISTANCE SCALE; COSMOLOGY: GRAVITATIONAL LENSING; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: 0957+561 full text sources ADS | data products SIMBAD (3) NED (2) Related Materials (1) Erratum: 1996ApJ...473..570G

Formation of Anisotropy in Galaxies

Since observations of elliptical galaxies show only a small fraction of gaseous matter, dissipationless N-body models are mainly used to follow the dynamical evolution of these systems. In order to end up with the observed de Vaucouleurs profile these models must be initially very cold which leads finally to a velocity distribution that is isotropic in the core and has a positive anisotropy A ≡ 1 − (σθ/σr)2 in the outer region (σθ, σr are the velocity dispersions in meridional and radial direction.). Contrary to these models, dissipative N-body simulations based on the idea of protogalaxies consisting of inelastically colliding clouds give negative anisotropics outside the core (see Figure). This dominance of circular orbits is caused by a combination of an orbit-dependent collision rate and a conservation of a negative anisotropy formed during the early collapse phase. Therefore, measurements of the anisotropy in galaxies can provide a tool for the study of the dissipative processes in the early galactic evolution.

Dense stellar cores in merger remnants

We use numerical models which include star formation to analyze the mass profiles of remnants formed by mergers of disk galaxies. During a merger, dissipation in gas and ensuing star formation leave behind a dense stellar core in the remnant. Rather than joining smoothly onto a de Vaucouleurs profile, the starburst population leads to a sharp break in the surface density profile at a few percent of the effective radius. While our results are preliminary, the lack of such signatures in most elliptical galaxies suggests that mergers of gas-rich disk galaxies may not have contributed greatly to the populations of present-day ellipticals.

The Shapes of Galaxy Groups

view Abstract Citations (12) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Shapes of Galaxy Groups Fasano, G. ; Pisani, A. ; Vio, R. ; Girardi, M. Abstract The shape of groups of galaxies has been since now a disregarded topic in the literature, mainly due to the fact that individual ellipticity estimates of poor systems are strongly biased toward higher values. Such a bias turns out to depend on both the ellipticity itself and on the richness of the group. In this paper we have devised a modified version of the classical Lucy's iterative method, which is able to perform a statistical rectification of the observed ellipticity distribution of groups. Since this method needs an estimate of the average radial profile of the groups, we have faced also this problem. Our analysis has been applied to a sample of 54 groups belonging to the Tully (1987) catalog. The sample is selected in order to reduce the well-known, distance-dependent observational biases, which are present in all available group catalogs (Pisani et al. 1992). We found statistical evidence that galaxy groups share a common law for the radial distribution of members. This law can be quite satisfactorily represented by a simple Gaussian model, whereas a de Vaucouleurs profile (for instance) is definitely not consistent with the data. It is important to stress that the rectified distribution of apparent ellipticities looks very different from the original (unrectified) one. This implies that any statistical analysis which does not take into account the above mentioned bias, has to give meaningless results. The final aim of the paper is to produce the distribution of intrinsic ellipticities of groups, by deprojection of their apparent (rectified) ellipticity distribution. To do this we have to assume a biaxial (oblate or prolate) intrinsic shape of the groups are some model for their spatial orientation. Because of this reason, before the deprojection, we have searched for possible alignments of the group major axes along the supergalactic plane or toward the Local Supercluster center. We found a weak indication in favor of the latter hypothesis, but more sizable samples are needed to give statistical significance to this conclusion. At this stage, we have been forced to perform the deprojection by assuming a random orientation of the groups in the space. The apparent (rectified) ellipticity distribution which is obtained from our sample of galaxy groups, turned out to be consistent with both the oblate and the prolate intrinsic shapes. However, the oblate hypothesis should imply that a great fraction of groups has a very flattened, disklike structure. This circumstance is rather difficult to be explained within the available cosmological scenarios. Moreover, the convergence of the deprojection algorithm in the oblate case is hard-earned, and the final agreement with the data is less satisfactory than that obtained in the prolate case. All these facts led us to prefer the prolate solution with respect to the oblate one. Obviously a mixture of two different populations (oblate and prolate), as well as a triaxial solution, cannot be excluded. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173256 Bibcode: 1993ApJ...416..546F Keywords: GALAXIES: CLUSTERING full text sources ADS | data products SIMBAD (1)

Globular clusters and cD formation - The case of M87

New wide-field CCD photometry around M87 is used to define the radial profile for its globular cluster system over the region 1'.2≤R≤9'.2. The best-fit de Vaucouleurs profile clearly shows an excess of clusters beginning at R∼4'.5, just where the cD envelope of the M87 halo begins. We find that this extra cD component of the globular cluster population has the same high specific frequency as the main body of M87 does; this result is used to argue for an epoch of cD envelope formation which precedes both astration of the envelope and relaxation of the Virgo Cluster itself

Diffuse light in dense clusters of galaxies. I - R-band observations of Abell 2029

An observing technique has been developed that uses a CCD detector, multiple overlapping exposures, and a tesselating algorithm that allows to do reliable differential photometry over a large field of view to a precision of 2 × 10 -4 of the night-sky level, limited only by statistical noise. The point-spread function of the telescope-detector combination has been measured out to 20' from the nominal pointing position. R-band observations are presented of the very dense cluster of galaxies Abell 2029. An elliptical component of diffuse light - extended halo of the cD galaxy - is detected with constant eccentricity of 0.9 that follows a de Vaucouleurs profile out to a distance of 425h -1 kpc [measured as d = (r min r max ) 1/2 )].

Determining mass-to-light ratios in elliptical galaxies

If the endstate of cooling hot gas in elliptical galaxies is a population of optically dark, low-mass stars near the galactic cores, the mass-to-light ratio could be expected to vary significantly with projected radius. No strong variation in M/L is observed. To investigate the sensitivity and reliability of observational mass-to-light determinations for a variety of galactic parameters, model galaxies having de Vaucouleurs profiles (but with central cores and outer cutoffs), variable velocity ellipsoid structure, and extended dark halos are constructed. Spurious radial variations in M/L can occur when none are present if the properties of the galactic models are processed similar to observational data. Conversely, when a population of diffuse dark stellar matter is added near the galactic cores, large gradients in M/L can escape detection. However, the magnitude of the central velocity dispersion and its variation with projected radius within the effective radius both suggest that a component of dark stars is unlikely to be more massive than about 30 times the core mass of luminous stars. This restriction is important in establishing the initial mass function of stars in elliptical galaxies and the history of winds and cooling inflows in the interstellar medium. 35 references.

The density profiles of tidally stripped galaxies

view Abstract Citations (117) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Density Profiles of Tidally Stripped Galaxies Aguilar, L. A. ; White, S. D. M. Abstract A simple model for collision-induced changes in the structure of a nonrotating spherical galaxy is presented, and its predictions are compared with N-body simulations. The numerical techniques, the evolution of the density profiles immediately after an encounter, and the relaxed state approached at late times are described. The De Vaucouleurs profiles are found to be very robust. Models whose initial surface densities are described by an r exp 1/4 law are still well fitted by such a law after collisions in which the target galaxy loses up to 40 percent of its mass. The tidal classes defined by Kormendy (1977) may be interpreted as a transient phenomenon produced by the tidal mixing of stars onto less bound orbits. The departure from an r exp 1/4 law evolves on the local dynamical time scale, and its radial position can be used to estimate the time since the tidal encounter. Although tidal encounters do not truncate density profiles, the isophotal radii of galaxies usually shrink. Publication: The Astrophysical Journal Pub Date: August 1986 DOI: 10.1086/164396 Bibcode: 1986ApJ...307...97A Keywords: Density Distribution; Galactic Clusters; Galactic Structure; Collisions; Many Body Problem; Radii; Tides; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: STRUCTURE; NUMERICAL METHODS; STARS: STELLAR DYNAMICS full text sources ADS |

Surface brightness and effective radius for elliptical galaxies

Seeing convolved two-dimensional de Vaucouleurs profiles have been fitted to digital images of the brightest elliptical galaxies in two nearby groups of galaxies and three clusters of galaxies with redshifts in the range 0.06 to 0.15. The digital images were created by scanning electronographic plates obtained by the use of several versions of the RGO electronographic camera. The linear relation between effective surface brightness ..mu../sub e/ and the logarithm of the effective radius r/sub e/, first discovered by Kormendy to be valid for nearby elliptical galaxies, is found to be equally valid for the largest and brightest galaxies in rich clusters of galaxies. The apparent universal nature of that relation indicates that the same type of processes might have been involved during the formation of all ellipticals from cD galaxies in clusters to fainter ellipticals in small groups. It is suggested that the (I/sub e/,r/sub e/) relation is not changed by the expected dynamical evolution of the brightest galaxies in clusters. If the cosmic nature of the (I/sub e/,r/sub e/) relation is confirmed by future observations, we suggest using the vertical position of that relation, derived from the brightest elliptical galaxies in rich clusters, as a new cosmological test, whichmore » should be independent of dynamical evolution.« less

Further observations of the elliptical galaxy NGC 5813

We have obtained the rotation curve and velocity dispersion profile along the major axis of the elliptical galaxy NGC 5813. The measurements extend out to almost 90 arcsec (≈ 16 kpc, taking H0 = 50 km s−1 Mpc−1) on either side of the centre of the galaxy. Surface photometry has also been obtained which reveals significant departures from the standard King (1966) or de Vaucouleurs (1959) profiles interior to 12 arcsec. The rotation curve is quite unusual. The peak velocity of 89 ± 7 km s−1 is reached at ≈ 3 arcsec from the centre, the rotational velocity then falls rapidly and remains roughly constant at 8 ± 2km s−1 between 10 and 80 arcsec. The velocity dispersion peaks at ≈ 10 arcsec and decreases at large and small radii. We compare the observations with simple dynamical models using the equations of stellar hydrodynamics (Binney 1980a). We show that the shape of the rotation curve may be qualitatively understood if the galaxy has highly anisotropic velocity dispersions in the outer parts, but the anisotropy vanishes in the central regions. The models predict velocity dispersion profiles which fall too steeply at large radii when compared to the observations. The discrepancy may be resolved if there exists a small increase in the mass-to-light ratio at large radii (less than a factor of 2 out to ≈ 90 arcsec). The models predict a decrease in the velocity dispersion towards the centre of the galaxy in rough agreement with the observations.